Organic dye effects on dense nonaqueous phase liquids (DNAPL) entry pressure in water saturated porous media

Visualization of DNAPL behavior in porous media is generally accomplished using three oil-soluble dyes: SudanIII, SudanIV, or Oil-Red-O. The dyes are generally assumed to not influence that behavior. That assumption was tested in the SudanIV-tetrachloroethene (PCE)-water-glass system. The dye significantly changes surface chemistry as a function of concentration and interface age. PCE mobility increases through lower adhesion tension. Increased mobility was demonstrated using entry pressure experiments for undyed and dyed PCE entering water-saturated glass bead media. Statistically significant entry pressure reduction occurred at a dye concentration of 0.0411 g/L, approximately two orders of magnitude lower than typically used. Dye type, concentration, and surface chemistry are therefore important experimental parameters which should be reported in multiphase flow studies. Dye use increases DNAPL surface chemical complexity, making them reasonable analogs for field DNAPLs. PCE entry pressure was strongly influenced by intrinsic permeability, providing experimental support for Bond number formulations which include permeability.